Exploration of Utulei Clarigester #1 for Facility Upgrade

Transcription

1 Pacific Design Build Corporation 1036 Mikole St. Honolulu, HI Phone #: (808) Fax#: (808) I. Objective: Exploration of Utulei Clarigester #1 for Facility Upgrade At the request of Lyon Associates Project Engineer, Ty Dempsey, Pacific Design Build Corporation entered into a subcontract contract to: 1. Inspect the existing clarigester #1 to determine whether it can be rehabilitated or replaced 2. Inspect the concrete of clarigester #1 to determine its structural integrity 3. Develop a methodology for rehabilitating the tank, if feasible. 4. Additional Scopes of Work (SOW) were a. Inspection of the headworks for suitability of comminutor and bar screen restoration b. Inspection of the influent wet well for suitability of installation of larger pumps c. Inspection of the effluent chlorine contact tank and piping for reduction of headloss II. Site Inspections: Lyon Associates made all travel arrangements and dispatched Pacific Design Build Corporation s principal engineer, Michael Weitzenhoff, to perform the inspections at the Utulei WWTP in American Samoa on February 21 st, Mr. Weitzenhoff met with American Samoa Power Authority (ASPA) Project Engineer Bob Davis on February 22, 2010 in order to confirm the SOW and for introduction to Fa i Mareko, Wastewater Operations Manager. Mr. Davis confirmed the objectives of the visit and Mr. Mareko offered the services of his staff to assist in the effort. Mr. Weitzenhoff conducted his first site inspection on February 22, The intent of the 1 st inspection was to compare the Utulei WWTP facilities with the drawings provided by Lyon Associates. Piping and facilities were confirmed to be largely in concurrence with the 60% Lyon Associates drawings dated February During this inspection, the following observations were recorded: The comminutor and bar rack, identified in earlier plant drawings, have been removed from the headworks. The hydraulic level in the headworks was within 4 of the top of channel

2 Clarigesters #3 and 4 have been provided with gas collection domes Separate FRP pipes convey influent from the headworks to each of the 4 clarigesters. These pipes and their fitting were examined and found to be in good condition The chlorine contact tank is actually 2 parallel structures with separate inlets and discharges to a common outfall/overflow weir On February 22, 2010 the entire facility, with the exception of clarigester #1, was found to be operating satisfactorily WWTP personnel performed routine maintenance and monitoring. The all appeared to understand their jobs and performed them safely The 2 nd day of field inspection focused on clarigester #1. This unit is out of service and drained. During this inspection, the following observations were recorded: The original Dorr Oliver clarigester motor drive with clarifier arms, scrappers, sludge mixing arms have been removed The external sludge mixer drive remains in place on the concrete deck but is completely wasted The external sludge mixer draft tube is corroded above and below grade The external sludge mixer draft tube upper connection to the digester is wasted and the lower connection has filled with debris The scum pit pump and telescoping valve have been removed The walkway mounted scum pit valves are in place however are frozen in position The scum box wash out drain line is broken below the box The sludge discharge line is disconnected outside the digester, at ground elevation The FRP weir and scum ring have been removed from the launderer The scum box and all associated components have been removed The top edge of the launderer box (which once had an interior facing, c shaped sheet metal insert) is spalling The floor of the launderer is rough but appears in good structural condition The effluent collection box from the launderer has a rough surface but appears structurally sound 2

3 The surface of the reinforced concrete structure of the clarifier and the digester sections are rough but appear to be in good structural condition Except for the top edge of the launder, the only significant spalling was observed in the reinforced deck column near the stair The double I beam and top checker plate that previously supported the drive motor and reduction gear for the clarifier and digester arms is wasted The structural supports for the double I beam appear structurally sound Piping through the reinforced concrete walls of the clarigester shows some interior degradation, but appear to remain functional The 2 manhole covers and cast in place seats that provide maintenance access from the clarifier zone to the digester zone have surface corrosion, but appear to remain functional Roof suspended mixing fingers in the digester section have corroded away or have been removed Access to the lower thrust bearing was impossible due to flooding in the digester compartment, however, it must be assumed to be wasted. The exterior galvanized support members of the maintenance walkway appear to be in good condition The wooden walkway and safety handrail are weakened in some areas The vertical ladders are stainless steel and are in good condition The exterior stairway is in good condition, except 1 reinforced concrete support column has spalling. III. Discussions with Plant Personnel: Discussions were initiated with the management and operational personnel of the Utulei Wastewater Treatment Plant in order to obtain their perspective regarding discussed facility upgrades. The plant is currently meeting its operational discharge requirements. The management of the facility feels that the rock basket is functioning adequately in removal of larger objects carried into the influent wetwell from the collection system. Some plastics, however, do escape the basket and carry over to the clarifier because they tend to float. The use of a comminutor was discussed with management. It was management s option that adding a comminutor at the headworks will not materially improve the 3

4 settleability of the influent and will add unnecessary maintenance and costs. Their position is supported by experience with the comminutor in the septage receiving pit. The comminutor chops debris into small pieces, but plastics continue to float, even when reduced in size. Further, these plastics carry over into the scum pit and then go to the digester where then tend to reform into large balls of plastic and grease. A mechanical, moving bar screen or other influent wetwell straining system could reduce plastic floating debris from reaching the clarifiers and the digesters. This would be beneficial in reducing scum and would improve the digestion process. This type of device and its location, however, are outside the scope of the currently envisioned upgrades. It is recommended, however, that this modification be considered in the near future. Both operation and management personnel were clear and unified in their request to have any upgrades to clarigester #1 match the mechanical system currently employed in clarigester #2. This will reduce the number of spare parts required for inventory and simplify operations. The installation of gas domes on clarigesters #3 and 4 were also identified as simple upgrades that could be applied to clarigesters #1 and 2. IV. Recommendations for Clarigester #1: 1. The clarigester s condition suggests rehabilitation rather than demolition and replacement. 2. Piping and mechanical systems for clarigester # 1 should be modeled after those in place on clarigester #2. Continued use of the Dorr Oliver design is recommended. 3. Installation of new components should utilize only type 316 stainless steel bolting hardware; including embedment into the concrete structure and fastening piping units together. 4. Areas of concrete spalling; e.g. top of launderer and support column, should be repaired in accordance with standard construction procedures. 5. All interior concrete surfaces should receive a coating of an appropriate epoxy compound to fill cracks, seal the surface and provide a smooth surface for proper hydraulics and to reduce maintenance associated with cleaning these surfaces. All exterior concrete surfaces should receive a coating of an appropriate concrete paint system to seal the surface and provide long term protection. 6. All walkway and handrail lumber should be removed and replaced with either FRP or other suitable non slip, UV resistant walkway material. Use of galvanized steel grating should be avoided. 4

5 V. Methodology for Clarigester #1 Rehabilitation: 1. Make contact with the Dorr Oliver representative and obtain a firm quote and recommendations and specifications for replacement of Clarigester mechanical components. The overhaul should address tank structural components, mechanical components and electrical components. Utilize these documents as part of the contract specifications. 2. Make contact with the Sika Corporation representative for concrete repair products and obtain recommendations and specifications for repair of concrete in wastewater services and for painting of concrete structures in moist, tropical environments. Utilize these documents as part of the contract specifications for concrete repairs (identified below). 3. Demo and remove the exterior sludge mixer drive from the concrete walkway. Repair the concrete deck allowing an opening for an 8 FRP pipe. Excavate the lower connection of the sludge mixer to Clarigester #1 wall. Demo and remove the entire sludge mixer unit. Repair and close the lower connection of the sludge mixer to the Clarigester. Modify the upper connection of the sludge mixer connection to the Clarigester by addition of an 8 FRP pipe. Extend 8 FRP pipe with elbow and vertical section through concrete deck, above, and terminate with 4 gas release pipe. 4. Demo and remove center Clarigester drive and gear mechanism. Demo and remove support I beams with associated handrail and decking. Examine and repair with high strength concrete any damage at I beam support areas. 5. Demo leading edge of concrete launderer channel to expose 1 st row of rebar. Restore concrete per ACI Concrete Repair Specification to create new launderer edge. Restore and plumb to original launderer channel elevation and make face ready for installation of FRP weir, per Dorr Oliver design. 6. Low pressure water blast (2500 to 3500 psi) all interior and exterior concrete surfaces in the clarigester including scum pit. Restore launderer channel, scum pit and all Clarigester interior surfaces with concrete repair product recommended by Sika Corporation. 7. Clear all debris from effluent discharge sump and confirm fitness of discharge piping. 8. Power tool clean cast iron manway seats (2) and manway covers embedded in floor of Clarigester. 9. Supply and install new scum pumps with hand off auto electrical controls. Existing scum piping may be reused, however replace 4 deck mounted ball valves with same size ball or plug valves (DeZurick). 5

6 10. Supply and install new telescoping valve and sleeve in scum pit to decant clarigester/remove sludge. 11. Supply and install 6 plug valve and piping on existing scum pit drainage to allow removal of clarigester sludge through scum pit to external tank truck. 12. Clear all debris from digester sludge box and underground pipe. Supply and install 6 plug valve and piping on clarigester sludge drain pipe to extend to external tank truck. 13. Supply and install new Dorr Oliver supplied fixed scum break fingers on roof of digester section of clarigester. 14. Supply and install new Dorr Oliver supplied I beam supports, walking surface, safety handrails and Clarigester center drive shaft with motor and gear mechanism. 15. Install new hand off auto electrical controls to Clarigester drive motor. 16. Supply and install Dorr Oliver vertical drive shaft and bottom thrust bearing. 17. Supply and install Dorr Oliver clarifier and digester scrappers and scum skimmer. 18. Supply and install Dorr Oliver effluent weir, scum shield and scum hopper. 19. Supply and install Dorr Oliver scum hopper in Clarigester and connect to 4 pipe in wall to scum pit. 20. Demo exterior wood walkway and wood handrail. Replace with FRP walking surface and aluminum handrail. 21. Utilize Dorr Oliver service technician for start up of unit. 22. Type 316 stainless steel bolting hardware should be maintained throughout all upgrade installations. VI. Other Project Objectives and Recommendations: 1. Influent wet well: The well remained flooded during all site visits, so it was impossible to determine whether adequate space is available to install 2 larger submersible pumps in place of the existing. Based on spacing of the guide rails, however, it appears that a moderate increase in pump size could be physically accommodated in the influent wet well. The electrical panel for the pumps was not examined, so the observer cannot comment on the adequacy of the power source for the pumps. 6

7 2. Headworks: The raised headworks were discussed earlier in this report. Installation of a comminutor and/or bar screen in this area is not recommended. The existing hydraulics suggest that even a 4 headloss caused by a screen or comminutor could result in an overflow of the structure s walls. Further, cleaning the screen in this elevated location could be dangerous, at worst, and clumsy, at best, with no place to dispose of the screenings. 3. Chlorine Contact Tank Flow Improvements: The following methodology is recommended for by passing the 16 bottleneck just prior to the chlorine contact tank and replacement with larger piping: a. Expose the effluent pipe from each Clarigester effluent pipe. b. Stop flow to each Clarigester sequentially and install a permanent Tee with a gate valve. c. Manifold the effluent from each Clarigester using 16 diameter or larger temporary HDPE pipe. Insert a magnetic flow meter in the 16 discharge pipe. Cut through the effluent weir box downstream of the plant effluent weir and discharge to the ocean outfall. d. While the bypass is in place, modify the influent and effluent piping of each chlorine contact tank to 24 diameter piping and connect to the upstream side of the effluent weir structure. e. After modification of the chlorine contact tank, normal effluent flow can be restored and the temporary HDPE pipe can be removed back to valve at the Tee. A blind flange should be installed on this valve to prevent leakage. Report prepared and respectfully submitted 1 March Michael Weitzenhoff, P.E. 7